Travelling shoring apparatus

ABSTRACT

A travelling shoring apparatus for inclined strata comprises two sets of shoes, one of which is situated on the working face and the other is situated on the side of the filling material, each shoe in a set being connected to a corresponding shoe of the other set by means of two double-acting shift rams 13, 14 fixed to the coupled shoes by means of universal joints 15 which determine, before and after shifting, a parallelogram 18, and by a connecting ram 16, the axis of which substantially coincides with the small diagonal of parallelogram 18. This shoring is used in particular for exploitation of inclined strata.

r wm

Unite atent 1 1 Alacchi June 4, 1974 TRAVELLING SHORING APPARATUS 22 Filed: Jan. 2, 1973 21 Appl. No.: 320,619

[56] References Cited FOREIGN PATENTS OR APPLICATIONS 1,126,821 4/1962 Germany 61/45 D 1,226,778 3/1971 Great Britain 1,213,019 11/1970 Great Britain 61/45 D Primary Examiner-Dennis L. Taylor Attorney, Agent, or Firm-Lewis H. Eslinger; Alvin Sinderbrand 5'7 ABSTRACT A travelling shoring apparatus for inclined strata comprises two sets of shoes, one of which is situated on the working face and the other is situated on the side of the filling material, each shoe in a set being connected to a corresponding shoe of the other set by means of two double-acting shift rams 13, 14 fixed to the coupled shoes by means of universal joints 15 which determine, before and after shifting, a parallelogram l8, and by a connecting ram 16, the axis of which substantially coincides with the small diagonal of parallelogram 18. This shoring is used in particular for exploitation of inclined strata.

9 Claims, 5 Drawing Figures PATENTEDJUN 419 4 SHEU 1 [IF 3 TRAVELLING SHORING APPARATUS The present invention relates to travelling shoring, used in mining, in particular for inclined strata, of the type comprising rear and forward sets of shoes, the forward set being situated on the same side as the working face and the rear set being situated on the same side as the embankment or filling material, each shoe in a set being connected to the corresponding shoe in the other set by means of a double-acting shift-ram which is fixed to each of the coupled shoes by means of a universal joint.

In travelling shoring of this type, in order to be able to move towards the working face, each shoe cooperates in the relaxed state, with the corresponding shoe in the other set. To achieve horizontal forward progress by the shoes and to prevent the shoes undesirably wandering off line either towards the top way or the bottom way, it has already been proposed to connect the shoes in each set together at their lateral extremity by a connecting ram one pair of which is hinged, to the upstream shoe, and the other pair to the downstream shoe. In known travelling shoring as hitherto constructed, each shoe can be guided along a horizontal shift or displacement path by the concerted cooperation of the connecting rams and the shift-ram which are able to act on the said shoes.

However, by reason of the hinged connection of each shoe to the adjacent shoes in the same set, this known travelling shoring does not give full satisfaction in use; in effect, to shift this shoring it is necessary to relax two shoes in the same set at once, so that the un-supported roof surface is relatively large, which can lead to collapses; furthermore, particularly due to the necessity of keeping the shoes to a horizontal shift path, the gap between two consecutive shoes in the same set must necessarily vary within wide limits; this entails, when the vein or seam is being worked by the "reversed working face" method, placing a flexible partition between each rear shoe on the side of the embankment which forms a connection between the individual shields carried by each of the rear shoes to prevent the material of the embankment entering the working through an opening resulting from the gap between one rear shoe and its neighbour. This flexible partition must be capable of providing a connection which is sealed against the embankment filling material, must allow all movements, both rotational and translatory, of one shoe with respect to its neighbour, and must fit the height of the working in which the shoring is used. Such a connecting partition therefore complicates the design and use of the known shorings hereinabove referred to.

It is an object of the invention to overcome or minimise these drawbacks and particularly by providing travelling shoring which is relatively simple in design and operation, in which the shaft path of the shoes is horizontal and which requires only one shoe to be released at a time in order to shift or displace it.

In accordance with the invention, therefore, each shoe in one set is also connected to the corresponding shoe in the other set, on the one hand, by a second shift-ram also fixed to the coupled shoes by means of universal joints which, when the two coupled shoes are mutually parallel, form a parallelogram with those associated with the first shift-ram, and on the other hand. by a rigid connecting member which is also fixed to the said shoes by means of universal joints, an extension of the axis joining the joints to the said shoes coinciding, at least approximately, with a diagonal of the parallelogram.

In such shoring according to the invention, there are no longer any joints between the consecutive shoes in the same set, so that, when the shoring is shifted, it will be sufficient to relax one single shoe at a time to enable it to move by the agency of the shift-rams. Moreover, as a result of the use of two shift-rams and a rigid connecting member, the control of the rams is simplified and may, moreover, be made automatic, since it is now no longer necessary to act concertedly on the various rams on the shoe to be moved and on the neighbouring shoes to achieve a'predetermined shift path as was necessary previously. In this new shoring, the mechanical connecting member performs the function of a tie-rod connecting two opposed corners of a parallelogram formed of hingedly connected rigid members; for this reason, this rigid connected member establishes the po sition of two successive corners of the said parallelogram, which corners form part of a relaxed shoe which is free with respect to the other two corners which form part of a fixed shoe; the rigid connecting member, particularlywhen it is arranged along the shorter diagonal of the aforementioned parallelogram, serves as a suspension or a support rod for the moving shoe to which it is connected and may thus support the majority of the weight of the said shoe if the inclination of the axis of the said tie-rod to the line of greatest slope is not too great.

The result is that the shift-rams in this new shoring no longer has to support a large part of the weight of the shoe during shifting so that their action on the latter is easier to control; this advantage of the shoring according to the invention is particularly useful when rear shoes are being shifted when the latter are subject to the pressure of the embodiment or filling material.

Other advantages and features of the invention will appear from a perusal of the description given below by way of non-limiting illustration, this description referring to the accompanying drawings in which:

FIG. 1 is a plan view, sectioned along line 1-1 of FIG. 2, of two coupled shoes according to one embodiment of the travelling shoring according to the inventron;

,FIG. 2 is an elevational section along the two-level line II-II through a rear shoe of the shoring shown in FIG. 1; and

FIGS. 3a to 30 show a schematic view of the various phases of shifting the travelling shoring according to the invention.

Referring now to the drawings, in FIGS. 1 and 3a to 3c, some of the shoes of the travelling shoring are shown in plan with respect to the wall of the vein or seam being worked.

As can be seen in FIGS. 3a to 3c the working face FT is inclined, by 35 for example, with respect to the greatest slope P of the seam. Furthermore, in the present case, the seam is being worked by the reversed working face" method, that is to say, in such a way that the filling material or embankment R overhangs the working face PT. The head way VT is situated at the upper limit of the working and the bottom way VB at referred to as the rear set SA, and a set of shoes B,, B B,, on the same side as the working phase FT and, which are referred to as the forward set SF. The two sets SA and SF are secured in a suitable fashion by their upper end shoes A,, B, at points C, and C to a support (not shown) provided in the head way VT.

Each shoe A,, A A,, in the rear set of shoes SA and each shoe 8,, B B,, in the forward set of shoes SF comprises a welded sheet-metal box ll, one compartment 1a of which, known as the support compart-' ment, is provided with a certain number, two for example, of cut-outs 2, to receive the same number of hydraulic props 3. As is known, each prop 3 is guided in attube which is mounted in the appropriate cut-out 2 of the support compartment la and which is connected to the said support compartment lla by means of two spring strips 5 lying one above the other. The spring strips 5 are held apart from one another and are fixed, on the one hand, in their central area to the support compartment la by the clamping action of central bolts 6 joining the said strips 5 to a connecting members 6a fixed to the support compartment la and also by their ends to the guided tube 4 by the clamping action of bolts 7. The lower end 8a of the cylinder 8 of the props 3 is held fast to a sliding runner 9 by means of a ball and socket joint 10, while the upper end 8b of the said cylinder 8 bears on the guide tube 4 through a return spring II, when the shoes are in the relaxed condition. At the upper end, the props 3 associated with the same tube carry a common head-piece or cap I2 which supports metal covering strips which are not shown.

As can be seen in FIGS. 1 and 3a to 3c, each of the shoes A, to A,, and B, to 8,, in the sets SA, SF is connected to the corresponding shoe in the other sets SF.

SA, according to the invention, on the one hand, by'

means of two double-acting shift-rams I3, I4 which are fixed to the shoes A, to A, and B, to B,, by means of universaljoints I5 so that their axes 13a, Ma are mutually parallel when the shoes A,-, B,-, which they connect, are themselves mutually parallel and, on the other hand, by means of a rigid connecting member such as a ram 16 which is also fixed to the shoes A, to A,, and B, to B,, by means of universal joints l7 and of which the axis 16a is inclined with respect to the axes 13a, 14a of the shift-rams l3, 14. The four joints 15 of the shiftram l3, 14 on the shoes A, to A,,, B, to B,, together form, both before and after shifting, the four corners of a parallelogram 18, two sides of which 18a, 181) are, in the example shown in the drawing, parallel to the longitudinal axis of the shoes A,, B, and therefore to the face FT of the working. The mechanical connecting ram- 16 is situated, in horizontal projection inside the parallelogram 38.

According to another embodiment, the rigid connecting member 16 may be formed by a tie-rod.

As can be seen more especially in FIGS. 3a to 3c, provision is made for positioning the joint 17 on coupled shoes A,-, B,-, such that, when the said shoes are in their position of maximum mutual separation, as shown in FIG. 3b in particular, the axis 16a of the corresponding connecting ram l6, after being suitably extended on either side, coincides substantially with the shorter diagonal of the parallelogram 18 formed by the joints 15. This particular arrangement of the joints l7 enables the ram 16, during the various phases of shifting, to support a large part of the weight of that one of the coupled shoes A,-, B, which is in the relaxed condition, as will be explained below. Furthermore, the travel of the shiftram 13, 14 is determined as a function of the angle that the latter forms with the longitudinal axes of the shoes A,, B,-, which axes are, in the present case, mutually parallel, and as a function of the inclination of the working face FT with respect to the greatest slope P, so that the angular sweep 6 of the axis 16a of the mechanical connecting ram 16 when one of the shoes A,, B, moves with respect to the other, has a bisector 16!; parallel to the greatest slope I. In this way, the shoes A,, B, are assured of a horizontal shift path as will be described below. It should be noted that it is possible to vary the angle formed by the axes 13a, 14a of the rams l3, 14 with the longitudinal axes of the shoes A,-, B,- by staggering one set of shoes with respect to the other laterally and parallel to its longitudinal axis.

In FIGS. 1 and 2, the support compartment la carries, at each of its lateral extremities, a pair of end bearings I9 for the shaft 20 of a joint body 21 itself used as a bearing for a second shaft 22, the member 20, 21 and 22 forming, in a manner known per se, a universaljoint l5joining shift-rams 13, 14 to shoes A,-, B,-. The

support compartment 1a also includes, as can be seen in the right hand portion of FIG. 2, on the same side as its free end next adjacent the coupled shoe B,- or A,-, two crosspieces of identical shape 23, lying one above the other, which extend parallel to the axis of the shoe A,, B,- and which have lugs 23a directed towards the coupled shoe B,- or A, and forming pairs of end supports 24 for the shaft 25 of ajoint-body 26 itself used as a bearing for another shaft 27, the member 25, 26 and 27, forming, in a manner known per se, a universal joint 17 joining the mechanical connecting ram 16 to a shoe A,, 8,.

According to a feature of the invention, the pairs of support 24 have multiple positions and the articulating shaft 25 of the body 26 may be mounted as desired between one of the pairs ofcorresponding mounting positions 24a, 24b, 24c, provided for on cross-pieces 23 so that it is possible to adjust the position of the joint 37 on the corresponding shoe A,-, B,- independently.

As can be seen in FIGS. 1 and 3a to 33 each shoe and in particular its head-piece or cap 12, seen in plan, has the general shape of a parallelogram arranged such that the seam being at an average angle, two opposite sides of the said parallelogram are substantially horizontal and therefore parallel to the general direction of the shift path, while the other sides are parallel to the working-face FT. This particular shape enables the shoes to support the roof of the working with the maximum bearing surface.

Each rear shoe carries a shield 28 which is adjustable in height when, as in the present case, the travelling shoring is used in a working having a reversed working face, that is to say when the embankment or filling material R is situated above the working.

In the case of the travelling shoring shown in the drawings and according to the invention, each rear shoe is fitted with an individual shield member 28 mechanically independent of the shield members carried by the other rear shoes. This shield member 28 comprises, in the present case, three pairs of fixed shaped posts 29 welded to the rear part of the box I associated with the shoe A,. These posts 29 reach to approximately the same height as the props in their withdrawn position (see FIG. 2). A first plate 30 is fixed to the posts 29 and forms the rigid and fixed part of the individual shield 28 and belonging to the shoe A,. It is possible to increase the height of this fixed part of the shield by fixing to the latter a heightening or extension plate 31 by means of three shaped fixing bars 32 which are firmly attached to the said plate 31 and which are each fixed between two posts 29 by means of pins 33 engaging in corresponding holes 34 provided in the posts 29 and in the fixing bars 32. The upper part of the shield 28 joining the front bar of the head piece or cap 12 of the front shoe A, at the upper edge 35 of the fixed part of the shield 28 is constituted for example ofa grid screen 36 fixed on the one hand to the cap 12 via an appropriate fixing member 37 welded to the cap 112, and on the other hand to the heightening or extension plate 31 through a fiat fixing strip 38 fixed to the upper end of the said extension plate 3i as will be seen on the drawing.

In conformity with the invention and as can be seen particularly in FIGS. 1 and 2, the shield 28 extends beyond the forward shoe A,- from the lateral end downstream of the compartment 1, parallel to the longitudinal axis of the said shoe A,-. For this purpose conveniently ribbed lateral extension plates 39 and 40 are fixed respectively to the side edge downstream of the fixed plate and the extension plate 31 and the fixing means 37, 38 as well as the grid screen 36 also extends laterally by the same length from the lateral extremity downstream of the compartment of of the shoe A,-.

In this manner, as can be seen in FIGS. 3a to 30, the downstream extension parts 39 and 40 as well as a lat eral extension zone of the grid screen 36 of each individual shield element 28 covers the lateral upstream extremity 28a of the shield element 28 carried by the forward adjacent shoe A,- 1 located downstream with reference to the shoe A,-.

In accordance with the particular embodiment of the shield element 28 as shown in FIGS. 3a to 36, the lateral downstream extremity of the said element 28 which extremity extends beyond the body of the front shoe A,- upon which the element 28 is fixed, is bent back towards the embankment or filling material R. This embodiment has the particular advantage of avoiding the deterioration of the said lateral down stream extremity by shocks on the adjacent shoe A,- ,t l at the end of the shifting path of the shoe A,-.

As can be seen more particularly in FIGS. 3a to 30, each shoe A,-, B,- of one and the other set SA, SF, is advantageously connected to the adjacent shoes of the same series SA or SF by the intermediary of a safety chain 41. Each chain 41 is fixed to the shoes A,-, B on the one hand for example upstream by the intermediary of a ram 42 which is located in a longitudinal compartment lb of a shoe A,-, B,-, whose axis is parallel to the longitudinal axis of the shoe A,-, B,- and which is fixed to the said compartment lb by ajoint 44 having an axis perpendicular to the axis of the ram 42 and on the other hand by the corresponding extreme link 41a, on a towing pin 45a fixed to the adjacent shoe A, B,- l of the same set SA, SF.

In FIGS. 30 to 30, there have been shown different stages in the shift path of the travelling shoring according to the invention. In FIG. 3a the shoes A,, A B B of the sets SA and SF are still in a position close to each other, the shifting rams I3, 14 being in the withdrawn position. In this same Figure the shoes 8;, and 8., have been shifted towards the new working face Fl", the corresponding shifting rams being in the extended position. This shifting movement is obtained, after the release of the shoes B and 8,, by the action of the shifting rams I3 and 14 of the shoes tending to separate the said shoes B B from the corresponding forward shoes A A During this displacement, the mechanical connecting ram 16 of the shoes A B and A Bg act as a suspension rod for the forward shoe B E the ram 16 is thus submitted to a tractive effort, the ram 16 carries out a rotational movement about its articulation 17 with the corresponding forward shoe A A through an angle 6 whose bisector 16b is parallel to the greatest slope P. It will readily be understood that if the angle 6 is not too large, for example if it is less than 40, the shifting rams l3 and 14 only have to support at the most about one third of the weight of the shoe B B and the course of the shift path for the said shoes B B is a circular are 0 whose maximum dimension is less than about 6 percent of the radius of the said are c. The shoes B B are thus submitted to the joint action of the corresponding shifting rams l3 and I4 and are supported by the corresponding rams 16, in such fashion that the said shoes B B are displaced so that their axis keeps the same direction. Moreover when the bisector of the angle 6 is parallel to P, the are c subtends a horizontally disposed chord in such a fashion that the new position of the shoes B B after shifting is on the same horizontal level as that of their old position represented in FIG. Bar by the dotted lines B;,, in such a fashion that the shifting trajectory is obtained horizontally without correction. Finally it is possible to adjust the amount of the displacement of the shoes B 8,, that is to say the shifting path of the shoring, by choosing the total path of the shifting rams I3 and I4; for the same rams l3 and 14, having a predetermined path, it is possible to adjust the position of the joints 17 of the mechanical connecting ram 16 on the corresponding shoe A A B 8,, by a convenient choice of the bearings 24a to 24d for mounting the articulation axes 25 hereinabove referred to in such a manner that the sweep angle 0 of the ram 16 shall always have an axis on a bisector I612 parallel to the greatest slope P.

In FIG. 3b, all the shoes B, to B of the forward set SF have been shifted towards the new working face FT whilst the shoes A to A of the forward set SA occupy their old position corresponding to the old working front FT in such a fashion that all the shoes A to A,,, B to B,, will be found in a maximum spacing position with reference to the corresponding shoe B to B or A, to A of the other set.

In FIG. 3c, it is proposed to shift the forward shoes A to A,,; in this Figure the shoes A and A, have already been shifted. During the shifting displacement, the mechanical connecting ram 16 of the shoes A B and A 8., now serve as a support bar subjected to contracting stresses in the direction of its axis. As in the case of FIG. 3a, the sweep angle 0 of the ram 16 has an axis on the bisector 16b parallel to the greatest slope P and consequently the path of the shifting travel for the shoes A A which are subjected to the joint action of the corresponding shifting rams 13, I4, and which are supported by the corresponding mechanical connecting ram 16, is a circular are d) which subtends a horizontal chord. Similarly, if the angle 0 isnot too big, the shifting rams 13 and 14 only have to support a very small fraction of the weight of the shoes A and A 4 and the maximum dimension of the are c is equal only to several per cent of the said radius of the are c. As a result the control of the displacement of the forward shoe B B is ensured with the maximum efficiency by the rams 13 and 14 Whatever be the pressure of the embankment or filling material R on the shield 28 of the said shoes B 8,. Moreover, during the shifting displacement of each forward shoe A,-, the constituents of the embankment or filling material cannot pass between the individual shields 28 and encroach on the markings due to the presence of the extension members 39 and 40 and of the corresponding lateral extension part situated above said elements 39, 410 of the grid screen 36. As may be seen in FIG. at the time of the retraction of a forward shoe A, with reference to the line of the preceding forward shoes A, to A the embankment or filling materials form a bank T from the downstream edge 28b of the shield 28 of the shoe A! We claim:

1. A travelling shoring apparatus for use in inclined strata between an embankment or filling material and a working face, said apparatus comprising rear and forward sets of shoes, said rear shoes having embankment engaging surfaces and said forward shoes having working face engaging surfaces spaced from and extending in a plane substantially parallel to said embankment engaging surface of the rear shoes, a first shift ram means for operatively connecting each shoe in each of said sets to the corresponding shoe in the other set, a second shift ram means extending substantially parallel to said first shift ram means for operatively connecting each shoe in each of said sets to the corresponding shoe in the other set thereby to define a parallelogram when the shoes in each set are parallel to each other, said first and second shift ram means lying in a substantially common plane extending generally perpendicularly to said embankment engaging surfaces and said working face engaging surfaces of the respective sets of shoes; a plurality of universal joints respectively connecting the opposite ends of said ram means to their associated shoes, rigid extensible connecting means operatively connected between corresponding rear and forward shoes in said sets, along an axis coinciding substantially with the diagonal of the parallelogram formed by said shoes and shift ram means, and universal joint means connecting the opposite ends of said connecting means to its associated shoes, whereby upon operation of said shift ram means, the perpendicular distance between said embankment engaging surfaces and said working face engaging surfaces is varied and said shoes are moved in a substantially straight line in a plane generally perpendicular to the plane of their faces.

2. Apparatus as claimed in claim 1, wherein the universal joints connecting saidrigid connecting means to said shoes are located in predetermined positions wherein both before and after the shifting of the shoes by said rams, the axisjoining the joints of said rigid connecting means defines an angle, with the line of greatest slope of the strata, which is equal to half the angular sweep of the said axis, said sweep accompanying a shifting displacement of one shoe.

3. Apparatus as claimed in claim 2 wherein at least one of the universal joints of the rigid connecting member is adjustably mounted on its associated shoe.

4. Apparatus as claimed in claim 3, wherein the rigid connecting means comprises a ram.

5. Apparatus as claimed in claim 3 wherein the rigid connecting means is a tie rod.

6. Apparatus as claimed in claim I wherein each shoe, in plan, has the general shape of a parallelogram whose opposite sides are parallel to the general direction of the shift path of the shoes.

7. Apparatus as claimed in claim 1 in which each shoe on the side of the filling material embankment is provided with a forward individual shield which is adjustable in height, said individual shield of each forward shoe extending beyond the downstream extremity of the body of said shoe thereby to cover the upstream lateral edge of the shield of the adjacent shoe.

8. Apparatus as claimed in claim 7 wherein the lateral downstream extremity of the individual shield of each shoe is bent back towards the embankment or filling material.

9. Apparatus as claimed in claim 1 wherein each shoe is connected to the following shoe of the same set by means of a safety chain, said chain having one end thereof fixed directly to one of the said shoes and the other end thereof fixed to the other shoe by means of a ram whose axis is parallel to the longitudinal axis of 

1. A travelling shoring apparatus for use in inclined strata between an embankment or filling material and a working face, said apparatus comprising rear and forward sets of shoes, said rear shoes having embankment engaging surfaces and said forward shoes having working face engaging surfaces spaced from and extending in a plane substantially parallel to said embankment engaging surface of the rear shoes, a first shift ram means for operatively connecting each shoe in each of said sets to the corresponding shoe in the other set, a second shift ram means extending substantially parallel to said first shift ram means for operatively connecting each shoe in each of said sets to the corresponding shoe in the other set thereby to define a parallelogram when the shoes in each set are parallel to each other, said first and second shift ram means lying in a substantially common plane extending generally perpendicularly to said embankment engaging surfaces and said working face engaging surfaces of the respective sets of shoes; a plurality of universal joints respectively connecting the opposite ends of said ram means to their associated shoes, rigid extensible connecting means operatively connected between corresponding rear and forward shoes in said sets, along an axis coinciding substantially with the diagonal of the parallelogram formed by said shoes and shift ram means, and universal joint means connecting the opposite ends of said connecting means to its associated shoes, whereby upon operation of said shift ram means, the perpendicular distance between said embankment engaging surfaces and said working face engaging surfaces is varied and said shoes are moved in a substantially straight line in a plane generally perpendicular to the plane of their faces.
 2. Apparatus as claimed in claim 1, wherein the universal joints connecting said rigid connecting means to said shoes are located in predetermined positions wherein both before and after the shifting of the shoes by said rams, the axis joining the joints of said rigid connecting means defines an angle, with the line of greatest slope of the strata, which is equal to half the angular sweep of the said axis, said sweep accompanying a shifting displacement of one shoe.
 3. Apparatus as claimed in claim 2 wherein at least one of the universal joints of the rigid connecting member is adjustably mounted on its associated shoe.
 4. Apparatus as claimed in claim 3, wherein the rigid connecting means comprises a ram.
 5. Apparatus as claimed in claim 3 wherein the rigid connecting means is a tie rod.
 6. Apparatus as claimed in claim 1 wherein each shoe, in plan, has the general shape of a parallelogram whose opposite sides are parallel to the general direction of the shift path of the shoes.
 7. Apparatus as claimed in claim 1 in which each shoe on the side of the filling material embankment is provided with a forward individual shield which is adjustable in height, said individual shield of each forward Shoe extending beyond the downstream extremity of the body of said shoe thereby to cover the upstream lateral edge of the shield of the adjacent shoe.
 8. Apparatus as claimed in claim 7 wherein the lateral downstream extremity of the individual shield of each shoe is bent back towards the embankment or filling material.
 9. Apparatus as claimed in claim 1 wherein each shoe is connected to the following shoe of the same set by means of a safety chain, said chain having one end thereof fixed directly to one of the said shoes and the other end thereof fixed to the other shoe by means of a ram whose axis is parallel to the longitudinal axis of the shoe. 